The invention relates to a plate valve which is sealed by corresponding surfaces on a valve seat of the valve housing and on the plate, which is connected to a valve spindle. A stroke of the valve spindle opens the valve and exposes a seal gap, which is usually radially symmetrically constructed, particularly in the shape of a truncated cone. The geometry of the flow in the seal gap and after exiting the valve decisively determines the continuing state of the liquid.
FIGS. 3 and 4 illustrate a typical plate valve according to the prior art in an axial section. This valve serves to generate a liquid cone spray. The liquid first flows axially in the annular gap 5 between a valve spindle 2 and the valve body 3 downward from above in the direction of the valve plate 3 and is deflected in the direction of a valve seat 4 which is incorporated into the valve body 1. Given an open valve, the liquid thus exits the valve gap (also referred to as a seal gap) which is located between the valve plate 3 and the valve seat 4 in the shape of a cone spray. This cone spray comprises a cone angle .alpha. which is pressed on by valve plate 3 and valve seat 4.
Previously common cone angles a of the plate seal face and cone angles .beta. of the valve seat face for generating a liquid-tight union have been selected equally large (.alpha.=.beta.). The problem regularly arises that, given an open valve, the flow cross-section, which is shaped like a truncated cone, in the seal gap 6 grows linearly with the radius (DI&lt;2R&lt;DA, with DI=inner diameter of the seal gap 6 and DA=outer diameter of the seal gap 6). The formula for the area, or respectively, cross-section A of the flow cross-section, which is shaped like a truncated cone, in the seal gap 6 derives from elementary geometrical considerations: EQU A=.PI..multidot.HA.multidot.sin(.alpha./2).multidot.(2R-0. 5HA.multidot.sin(.alpha.))
with HA=outer height of the gap.
In the prior art, with .alpha.=.beta., the difference between the outer height HA of the gap 6 and the inner height HI of the gap 6 corresponds to the stroke executed by the valve spindle.
With dimensions that are typical in fuel injection valves, the following applies: inner diameter DI=4 mm; outer diameter DA=4.5 mm.
A relative change derives of the minimal flow cross-section from the inflow of the liquid to the outflow of the liquid in relation to the valve gap, or respectively, seal gap 6, which can be calculated accordingly: EQU (DA-DI)/(DI-0, 5HA.multidot.sin(.alpha.)).apprxeq.0.5/4=0.125=12.5%.
In the open condition, the cone spray valve thus represents a diffusor. Such a sharp increase of the flow cross-section over such a short distance leads to a heavily delayed flow and to cavitation. Such cavitation has already been experimentally observed in injection valves with a seal face such as is described above. Given the decompression from ca. 200 bar to 1 bar, which corresponds to 2%, the volume increase cannot compensate this geometric expansion of the traversed cross-section by means of the liquid itself, whose compressibility is .kappa.=10.sup.-9 m.sup.2 /N, particularly in fuels,. For this reason, this sharp drop in pressure is associated with vaporization phenomena and cavitation.